IKImageBrowserView 延迟加载？

Question

为了使用IKImageBrowserView，必须使用以下方法实现数据源

– numberOfItemsInImageBrowser:
– imageBrowser:itemAtIndex:

这与具有以下数据源方法的NSTableView没有什么不同，

– numberOfRowsInTableView:
– tableView:objectValueForTableColumn:row:

但是，令人不安的区别是而 NSTableView 在调用 之前会考虑当前可见的内容 - tableView:objectValueForTableColumn:row:，IKImageBrowserView 似乎会迭代在 – numberOfItemsInImageBrowser: 中给出的整个范围内，并要求 imageBrowser:itemAtIndex:。不幸的是，数据源有时由数十万个项目支持，加载所有不必要的项目是一种可怕的浪费。无论如何，有没有办法让 IKImageBrowserView 只加载可见的项目（当然是预加载），就像 NSTableView 那样？

更新

我尝试编写一个 NSProxy 子类，它确实有效。 （好吧，稍后会详细介绍）它看起来像这样

// .h file

#import <Foundation/Foundation.h>

@interface ILArrayItemProxy : NSProxy

- (id)initWithArray:(id)array index:(NSUInteger)index;

+ (id)proxyWithArray:(id)array index:(NSUInteger)index;

@end

// .m file

#import "ILArrayItemProxy.h"

@interface ILArrayItemProxy() {
    id _array;
    NSUInteger _index;
}

@property (readonly) id target;

@end

@implementation ILArrayItemProxy

- (id)initWithArray:(id)array index:(NSUInteger)index {
    _array = array;
    _index = index;
    return self;
}

- (id)target {
    return [_array objectAtIndex:_index];
}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)sel {
    return [self.target methodSignatureForSelector:sel];
}

- (void)forwardInvocation:(NSInvocation *)invocation {
    [invocation invokeWithTarget:self.target];
}
+ (id)proxyWithArray:(id)array index:(NSUInteger)index {
    return [[ILArrayItemProxy alloc] initWithArray:array index:index];
}

@end

现在，当 imageBrowser 请求 – imageBrowser:itemAtIndex: 时，我会返回

[ILArrayItemProxy proxyWithArray:self.arrangedObjects index:index];

这非常有效！确实实现了延迟加载，并且我不再立即从存储中检索所有对象。然而，在任何视图上调用 reloadData 时，问题就会随之而来。

这是来自 NSTableView IKImageBrowserView 的错误消息，

Cannot update for observer <NSAutounbinderObservance 0x105889dd0> for the key path 
"objectValue.status" from <NSTableCellView 0x105886a80>, most likely because the value
 for the key "objectValue" has changed without an appropriate KVO notification being sent.
 Check the KVO-compliance of the NSTableCellView class.
2012-01-29 11:48:01.304 [62895:707] (
    0   CoreFoundation                      0x00007fff92bf6286 __exceptionPreprocess + 198
    1   libobjc.A.dylib                     0x00007fff91d3ad5e objc_exception_throw + 43
    2   CoreFoundation                      0x00007fff92bf60ba +[NSException raise:format:arguments:] + 106
    3   CoreFoundation                      0x00007fff92bf6044 +[NSException raise:format:] + 116
    4   Foundation                          0x00007fff9154b519 -[NSKeyValueNestedProperty object:withObservance:didChangeValueForKeyOrKeys:recurse:forwardingValues:] + 689
    5   Foundation                          0x00007fff9154986f NSKeyValueDidChange + 186
    6   Foundation                          0x00007fff914f60fb -[NSObject(NSKeyValueObserverNotification) didChangeValueForKey:] + 130
    7   AppKit                              0x00007fff90a2c26d -[NSTableRowData _addViewToRowView:atColumn:row:] + 434
    8   AppKit                              0x00007fff90a2bf81 -[NSTableRowData _addViewsToRowView:atRow:] + 200
    9   AppKit                              0x00007fff90a2abe3 -[NSTableRowData _addRowViewForVisibleRow:withPriorView:] + 404
    10  AppKit                              0x00007fff90a2a9e2 -[NSTableRowData _addRowViewForVisibleRow:withPriorRowIndex:inDictionary:withRowAnimation:] + 184
    11  AppKit                              0x00007fff90a2a928 -[NSTableRowData _addRowViewForVisibleRow:] + 38
    12  AppKit                              0x00007fff90a2a06c -[NSTableRowData _unsafeUpdateVisibleRowEntries] + 448
    13  AppKit                              0x00007fff90a29e87 -[NSTableRowData updateVisibleRowViews] + 95
    14  AppKit                              0x00007fff909c1c56 -[NSTableView viewWillDraw] + 156
    15  AppKit                              0x00007fff90924c11 -[NSView viewWillDraw] + 666
    16  AppKit                              0x00007fff90924c11 -[NSView viewWillDraw] + 666
    17  AppKit                              0x00007fff909254a2 -[NSScrollView viewWillDraw] + 43
    18  AppKit                              0x00007fff90924c11 -[NSView viewWillDraw] + 666
    19  AppKit                              0x00007fff90924c11 -[NSView viewWillDraw] + 666
    20  AppKit                              0x00007fff90924c11 -[NSView viewWillDraw] + 666
    21  AppKit                              0x00007fff90924f7b -[NSSplitView viewWillDraw] + 67
    22  AppKit                              0x00007fff90924c11 -[NSView viewWillDraw] + 666
    23  AppKit                              0x00007fff90924c11 -[NSView viewWillDraw] + 666
    24  AppKit                              0x00007fff90924c11 -[NSView viewWillDraw] + 666
    25  AppKit                              0x00007fff90924f7b -[NSSplitView viewWillDraw] + 67
    26  AppKit                              0x00007fff90924c11 -[NSView viewWillDraw] + 666
    27  AppKit                              0x00007fff90924c11 -[NSView viewWillDraw] + 666
    28  AppKit                              0x00007fff90923952 -[NSView _sendViewWillDrawInRect:clipRootView:suppressRecursion:] + 1358
    29  AppKit                              0x00007fff909226c1 -[NSView displayIfNeeded] + 1039
    30  AppKit                              0x00007fff9091e6fa -[NSAnimationManager animationTimerFired:] + 2593
    31  Foundation                          0x00007fff91537014 __NSFireTimer + 102
    32  CoreFoundation                      0x00007fff92baaf84 __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 20
    33  CoreFoundation                      0x00007fff92baaad6 __CFRunLoopDoTimer + 534
    34  CoreFoundation                      0x00007fff92b8b471 __CFRunLoopRun + 1617
    35  CoreFoundation                      0x00007fff92b8aae6 CFRunLoopRunSpecific + 230
    36  HIToolbox                           0x00007fff8cdf63d3 RunCurrentEventLoopInMode + 277
    37  HIToolbox                           0x00007fff8cdfd58f ReceiveNextEventCommon + 181
    38  HIToolbox                           0x00007fff8cdfd4ca BlockUntilNextEventMatchingListInMode + 62
    39  AppKit                              0x00007fff908e63f1 _DPSNextEvent + 659
    40  AppKit                              0x00007fff908e5cf5 -[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:] + 135
    41  AppKit                              0x00007fff908e262d -[NSApplication run] + 470
    42  AppKit                              0x00007fff90b6180c NSApplicationMain + 867

另一方面，如果我要调用它的 reloadData，它就会挂在我身上，而不会出现任何类型的错误消息>。

是的，我成功地用一个问题替换了另一个问题，这就是生活吗？